Session setup in an energy-efficient cellular wireless telecommunications system

ABSTRACT

The invention relates to a telecommunications system comprising at least a plurality of SA-cells. The invention provides a method for a terminal to facilitate establishment of a data connection between the terminal and at least one of the SA-cells. The method includes steps of, while the terminal is in an idle mode, the terminal transmitting an information request message (IRM) for the plurality of SA-cells and receiving, from each SA-cell of one or more SA-cells of the plurality of SA-cells, a message comprising at least information indicative of a strength with which the each SA-cell received the IRM. The method further includes the step of, at least partially based on the messages received from the one or more SA-cells, the terminal selecting an SA-cell of the plurality of SA-cells for establishing the data connection between the terminal and the selected SA-cell.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/344,292, filed Sep. 12, 2012, which is the U.S. National StageApplication of International Application No. PCT/EP2012/067864 filed onSep. 12, 2012, published in English, which claims priority under 35U.S.C. § 119 or 365 to European Application No. 11181162.6, filed Sep.13, 2011.

FIELD OF THE INVENTION

Generally, the invention relates to the field of wirelesstelecommunications. More specifically, the invention relates to thefield of establishing a data connection between a terminal and a cell inan energy-efficient cellular wireless network.

BACKGROUND OF THE INVENTION

A cellular wireless access telecommunications network (system) typicallyincludes multiple base stations, also known as, for example, baseterminal station in GSM, NodeB in WCDMA (UMTS), and evolved NodeB or eNBin LTE. A base station includes at least transmitting and receivingequipment to support wireless communication with a (possibly mobile)terminal, in standardization more formally known as UE (User Equipment).The range that can be covered with the transmitter/receiver in a basestation is limited. The area that can be served by thetransmitter/receiver of a base station is referred to as its “coveragearea” or as the “cell.” As used herein, the term “cell” refers to boththe base station itself and to its associated coverage area.

A cell (base station) in a cellular network is typically connected tothe remainder of the network via one or more backhaul links, forexample, via optical fiber, via copper wire or wirelessly. A basestation further includes processing capabilities, for example for thewireless transmission and reception and for handling the protocolsspecified between the base station and the terminal and between the basestation and the network, including other cells.

In a cellular network, different cells may have different sizes,indicated e.g. as macrocells, microcells, picocells or femtocells indecreasing order of cell size. Cells may show a partial overlap withnearby cells or a smaller cell (e.g. picocell) may be entirelyoverlapped by a larger cell (e.g. macrocell). Multiple cells may thusform a cellular network providing near contiguous coverage in a verylarge area.

In a cellular network it is common that each cell (base station), whenin operation, transmits broadcast signals. Such signals are known as,for example, BCH (Broadcast CHannel) in GSM, as CPICH (Common PilotCHannel) in WCDMA (UMTS) and as RSs (Reference Signals) in LTE. The sameor separate broadcast signals are used to indicate a cell's (basestation's) presence and to broadcast information about the cell (systeminformation), for example, the cell identity and information about theconfiguration of the cell and/or about the cell's resources, such ase.g. which channel to use in order to initiate contact with the cell.Such broadcast signals allow terminals to make measurements on thebroadcast signals, e.g. to determine the strength of the signal receivedby the terminal, and to receive the cell's system information. Thebroadcast signals are usually transmitted as long as the cell is inoperation. The transmit power involved in broadcasting these signals mayconsume up to 20% of the cell's maximum transmit power, also when thecell does not actually exchange data with a terminal in the cell or whenthere is no terminal at all in the cell.

In a cellular wireless network it is common to distinguish a terminal tobe in an ‘idle mode’ or in an ‘active mode’. In the active mode, theterminal is able to exchange data (e.g. sending/receiving an e mail ormaking a phone call) via a cell in which the terminal is located. Thisrequires resources in the network (e.g. frequencies and/or codes) andalso requires the terminal and the network to provide power for thepurpose. In the idle mode the terminal is not able to exchange data and,therefore, does not require the above resources and consumes less power.A terminal in the idle mode only regularly listens to signals broadcastby the cells and selects a ‘best cell’, for example the cell with thesignal that the terminal receives as strongest. A terminal in the idlemode also monitors the paging channel transmitted by the selected cellfor a paging message addressing the terminal. Such an (idle mode)terminal is said to ‘camp on’ the selected cell. When, for examplebecause of terminal mobility, a different cell is identified as bestcell, the terminal may re-select the different cell as ‘best cell’ andcamp on the newly selected cell. It should be noted that a terminal inthe idle mode normally does not inform the cell and/or the network aboutwhich cell the terminal is camping on, also not when re-selecting adifferent cell as best cell. When the terminal re-selects to a cellwhich is found to be in a different location area (LA or RA—routingarea), which the terminal may determine from the cell's systeminformation, then the terminal initiates contact with the network viathe newly selected cell to perform an LA or RA update procedure, andsubsequently returns to the idle mode. Thus, the network is made awareof the LA/RA the idle terminal is located in. A LA/RA commonly comprisesmultiple cells, as configured by the network operator. Consequently, thenetwork is not aware on which cell an idle mode terminal is camping on,it is only aware in which LA/RA an idle terminal is (expected to be)located.

In a cellular wireless access telecommunications network a terminal andthe network need to set up a session when the terminal requests aservice or is being paged. This involves a terminal in the idle modemaking a transition to the active mode. In an LTE network, for example,a session setup is a two-step process, the result of which isillustrated in FIG. 1. If service is initiated by the network, thenetwork performs a paging procedure, where a paging message is broadcastin all cells where the network expects the terminal to be camping on(RA/LA). When the terminal receives a paging message addressing theterminal, or if service is initiated by the terminal without having beenpaged, in a first step the terminal performs a random access channel(RACH) procedure towards the cell it currently is camping on toestablish a Radio Resource Control (RRC) connection. When successful, inthe second step, the RRC connection with that cell is used to negotiateresources for and to establish a data connection between the terminaland that cell. Then the wireless exchange of user data between theterminal and the cell is possible. 3GPP TS 36.213 and 3GPP TS 36.331describe these procedures in more detail.

As is illustrated in FIG. 1, for the LTE network as well as for otherlegacy networks such as e.g. GSM and UMTS, all transmissions, be itsignalling or data, occur between the terminal and a single cell whichis the same cell that the terminal was camping on when it was in idlemode.

Recently, a new, more energy efficient, network architecture is beingdeveloped. One aspect in the new architecture is the use of relativelysmall cells. High bit rate data connections can be much more efficientlyprovided with a larger number of (at least partially overlapping) smallcells (e.g. microcells, picocells, femtocells) than with a fewer numberof larger cells (e.g. macrocells). A further aspect in the newarchitecture is that the power consumption of a cell is envisioned toscale, as much as possible, with the service actually provided (e.g.with the number of active terminals served, with the bit rate providedto a terminal, with the distance covered by the connection to aterminal, etc.). One approach for realizing this vision includes puttingthose cells that do not actually serve an active terminal into apower-save mode, e.g. switching those cells almost completely off.Another, complementary, approach includes significantly reducing orrefraining from transmitting broadcast signals that are common inconventional networks. The transmission of these broadcast signalscauses a large overhead, in particular for cells operating at less thanfull load.

The new architecture envisions distinguishing between different types ofcells. A first type of cells, in this text referred to as ‘SA-cell’ isprimarily optimized to support the wireless exchange of data with activeterminals. The energy-efficiency improvements as outlined above arefocused on the SA-cells. A second type of cells, in this text referredto as ‘LA-cell’ is primarily optimized for other functions in a cellularnetwork, including those also found in conventional networks. Thus, itis envisioned to reduce the overhead in the system to that attributed tothe LA-cells.

An LA-cell typically covers a larger area, for example comparable tothat of a conventional macrocell. The LA-cells together provide nearcontiguous coverage in the area desired to be covered, much like in aconventional network. An LA-cell may transmit broadcast and systeminformation, much like a conventional cell; an idle terminal may camp onan LA-cell and may also initiate a signalling connection with theLA-cell, e.g. to perform an LA/RA update or to detach from the network.

An SA-cell covers a smaller area, for example comparable to that of aconventional microcell, picocell or femtocell. The SA-cells together maysupport a certain bit rate in the near-contiguous area desired to becovered. An SA-cell only transmits signals when and in so far it isneeded; it may be regarded to be normally ‘off’ or in a power-save orstand-by mode. An idle terminal also does not camp on an SA-cell.Although such a network has been referred to as a “Beyond Cellular GreenGeneration” (BCG2) network, this term may change in the future.Therefore, in the context of the present application, a network havingsuch architecture will be referred to as an “energy-efficient cellularwireless network.”

The result of a session setup in an energy-efficient cellular network isillustrated in FIG. 2. If session setup is network-initiated, this ispreceded by the terminal receiving a paging message via the LA-cell itis camping on. As shown, the session setup in an energy-efficientcellular network may be sub-divided into two parts. The first partincludes the establishment of a signalling connection between theterminal and the LA-cell it currently is camping on, which may include aRACH procedure and RRC connection set-up, similar to legacy networks.After a signalling connection between the terminal and the LA-cell hasbeen established, the second part includes the establishment of a dataconnection (data session) with an appropriate SA-cell.

Note that, in an energy-efficient network according to thisarchitecture, it may sometimes not be possible to identify anappropriate SA-cell immediately. This may happen e.g. because allSA-cells in the vicinity of the terminal may be in a power-save mode anddo not transmit a suitable signal. It may also be the case that someSA-cell is active and that the terminal detects a suitable signal fromthe SA-cell, but that the active SA-cell cannot optimally support therequested data session from an energy saving perspective (e.g. there isan inactive SA-cell in a better position, e.g. much closer to theterminal). It may also be the case that some SA-cell is active but thatthe active SA-cell cannot optimally support the requested data sessionfrom a quality of service (QoS) perspective (e.g. the active SA-cellcannot support the data session with the requested bit rate, while otherinactive SA-cell(s) can).

As can be seen from FIGS. 1 and 2, setting up a session in a networkaccording to this new architecture is different from that in legacynetworks. One difference is that the terminal issues a request messageto a ‘best cell’ an idle terminal is camping on but that this cell is,normally, not going to serve the terminal (i.e., the data connection forexchanging the actual user data is set up with another cell). Anotherdifference is that the SA-cell's RAT (Radio Access Technology) tosupport the data connection need not be the same as the LA-cell's RAT tosupport the terminal in idle mode, which allows optimization of one orboth RATs separately for their respective primary purposes. Yet anotherdifference is that, in the new architecture, the ‘best cell’ to supportthe data connection still needs to be found. Consequently, as a part ofthe session setup procedure in an energy-efficient network, anappropriate cell (SA-cell) needs to be selected to support the dataconnection with the terminal. To ensure high quality and/or userexperience, the session setup, which includes both identifying anappropriate cell and establishing a data connection with it, ispreferably performed quickly.

As the foregoing illustrates, what is needed in the art are methods andsystems for facilitating establishment of a data connection between aterminal and a SA-cell in an energy-efficient network, such as e.g. aBCG2 network.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, in atelecommunications system comprising at least an LA-cell and a pluralityof SA-cells, a method for a terminal to facilitate establishment of adata connection between the terminal and at least one of the pluralityof SA-cells is provided. The method includes, while the terminal is inan idle mode and is camping on the LA-cell, the terminal transmitting aninformation request message (IRM) for the plurality of SA-cells andreceiving, from each SA-cell of one or more SA-cells of the plurality ofSA-cells, a message comprising at least information indicative of astrength with which the each SA-cell received the IRM. The methodfurther includes based, at least partially, on the messages receivedfrom the one or more SA-cells, selecting an SA-cell of the plurality ofSA-cells for establishing the data connection between the terminal andthe selected SA-cell. Preferably, the telecommunications systemcomprises a cellular wireless access telecommunications system.

In the context of the embodiments of the present invention, theexpressions “LA-cell” and “SA-cell” are used to differentiate betweentwo different types of cells.

The first type of cell, the LA-cell (Large Area cell), refers to a cellthat is able to cover a larger area with a smaller bit rate, as comparedwith the second type of cell. The LA-cell is primarily intended forcarrying signaling messages from/to a terminal, e.g. the LA-cell isintended to at least be able to page a terminal. A terminal in idle modemay further be assumed to ‘camp’ on at least one of these LA-cells.While the LA-cell is not primarily intended to be used to carry wirelessuser data from/to a terminal, it is not precluded that other signalingthan paging or that also some user data is carried via an LA-cell. Inthe intended coverage area of the wireless access network it may beassumed that at least one LA-cell is fully operational or, in otherwords, an LA-cell is ‘normally on.’

The second type of cell, the SA-cell (Small Area cell), refers to a cellthat is able to cover a smaller area with a higher bit rate, as comparedwith the LA-cell. The SA-cell is primarily intended to carry user datafrom/to a terminal over the established data connection (i.e., theSA-cell is primarily intended to handle connections with activeterminals). Yet, it is not precluded that also some other informationand/or some signalling is carried via an SA-cell. In the intendedcoverage area of the wireless access network it may be assumed that atleast one SA-cell is able to provide coverage. An SA-cell is only fullyoperational when and to the extent that it is needed or, in other words,an SA-cell is ‘normally off.’

According to various embodiments of the present invention, the SA-cellsmay occur in any mix of frequency bands and/or radio access technologies(RATs). It is also not precluded that there are differently sizedSA-cells (e.g. macro, micro, pico and femto SA-cells, with or without ahierarchical organization), where larger SA-cells may e.g. moreefficiently serve highly mobile terminals.

As used herein, the expression “data connection between a terminal andan SA-cell” refers to a communication path for a wireless exchange ofuser data between the terminal and the SA-cell. The communication pathfor user data, including the section between the terminal and theSA-cell, is usually set up according to a set of parameters, forexample, depending on what type of user data needs to be exchanged (e.g.for sending/receiving e-mail, for making a voice or video call, etc.).The set of parameters, commonly referred to in the art as “QoSparameters” or “QoS profile,” may include parameters such as e.g.maximum bitrate, guaranteed (minimum) bitrate, bit error ratio anddelay/latency.

In contrast, signalling messages exchanged between the terminal and theLA-cell do not contain user data and are exchanged between e.g. theterminal and various entities in the telecommunication system.Signalling messages may be exchanged without establishing a connectionor via a “signalling connection” with a modest bit rate and with aquality sufficient for most signalling information to arriveuncorrupted. A signalling connection, when used, is to a large extentalso independent of the parameters of the “data connection” it may beassociated with.

Further, it is understood that the terms “user data” and “user terminal”do not necessarily imply a presence of a human user and the embodimentsof the present invention may also be applicable to e.g. a smartphonechecking e-mail without human intervention and to machine-to-machine(M2M) communications. The term “user data” is merely used todifferentiate between the actual data that is to be exchange over thedata connection and the signaling.

As described herein, a terminal may be either in an “active mode” or an“idle mode.” As used herein, the expression “a terminal in an idle mode”refers to a terminal that is neither exchanging user data nor able toexchange user data but is camping on a LA-cell and is monitoringpossible paging messages for the terminal from the LA-cell. In otherwords, the expression “a terminal in an idle mode” is used to describe aterminal which does not have support for the wireless exchange of userdata between the terminal and an SA-cell. In contrast, the expression “aterminal in an active mode” refers to a terminal that is eitherexchanging user data or able to exchange user data via at least oneSA-cell. In other words, an active terminal supports or is able tosupport the wireless exchange of user data between the terminal and theSA-cell(s). These notions of idle mode and active mode may be comparablewith like notions in standardized conventional networks but do notnecessarily coincide exactly with standardized definitions.

In an embodiment, the IRM comprises a request for establishing the dataconnection between the terminal and one of the plurality of SA-cellsand, optionally, further comprises an indication of a service requestedby the terminal and/or an indication of terminal's capabilities.

In an embodiment, the IRM is transmitted more than once.

In an embodiment, the IRM is transmitted upon receiving an indicationthat the data connection between the terminal and one of the pluralityof SA-cells is to be established, and/or in a predetermined pattern.

In an embodiment, the method further comprises establishing the dataconnection between the terminal and the selected SA-cell.

According to another aspect of the present invention, an LA-cellconfigured for use in the methods described herein is disclosed. TheLA-cell is configured at least for providing a transmit-trigger to theterminal instructing the terminal to transmit the IRM and/or providing areceive-trigger to at least one of the plurality of SA-cells to enter anIRM listening mode, wherein in the IRM listening mode the at least oneof the plurality of SA-cells is capable of receiving the IRM, wherein,optionally, the receive-trigger is provided in response to receiving aservice request message from the terminal.

According to another aspect of the present invention, an SA-cellconfigured for use in the methods described herein is disclosed. TheSA-cell is configured at least for determining the strength with whichthe SA-cell received the IRM and providing to the terminal the messagecomprising at least information indicative of the determined strength.

In an embodiment, the SA-cells provides the message to the terminal morethan once.

In an embodiment, the SA-cell is further configured for providing themessage using a channel code assigned to the SA-cell and/or forincluding in the message an identification of the SA-cell.

In an embodiment, the SA-cell is configured for entering an IRMlistening mode at predetermined times, e.g. periodically, wherein in theIRM listening mode the SA-cell is capable of receiving the IRM.

In an embodiment, the SA-cell is configured for entering the IRMlistening mode in response to receiving a receive-trigger from theLA-cell, the receive-trigger instructing the SA-cell to enter the IRMlistening mode, where the receive-trigger is provided to the SA-cell inresponse to the LA-cell receiving a service request message from theterminal and/or in response to the LA-cell receiving a request totransmit a paging signal to the terminal.

In an embodiment, the SA-cell is further configured for receiving anindication that the data connection is to be established between theSA-cell and the terminal.

According to other aspects of the present invention, a terminal, acomputer program with portions (possibly distributed) for performing thevarious functions described herein, a data carrier for such softwareportions, and a telecommunications system are disclosed. Thetelecommunications system may include two or more of the terminal, theLA-cell, and the SA-cell as described herein.

According to yet another aspect of the present invention, in atelecommunications system comprising at least a first SA-cell and one ormore additional SA-cells, a method for a terminal in an active mode tofacilitate handover of a first data connection to a second dataconnection is disclosed. The first data connection is a data connectionbetween the terminal and the first SA-cell. The second data connectionis a second data connection between the terminal and a second SA-cell ofthe one or more additional SA-cells. The method includes the terminaltransmitting an IRM for the one or more additional SA-cells andreceiving, from each SA-cell of one or more SA-cells of the one or moreadditional SA-cells, a message comprising at least informationindicative of a strength with which the each SA-cell received the IRM.The method also includes the terminal, based, at least partially, on themessages received from the one or more SA-cells, selecting the secondSA-cell of the one or more additional SA-cells.

Hereinafter, embodiments of the invention will be described in furtherdetail. It should be appreciated, however, that these embodiments maynot be construed as limiting the scope of protection for the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic illustration of the result of a session setup inlegacy networks;

FIG. 2 is a schematic illustration of the result of a session setup inan energy-efficient network, according to an embodiment of the presentinvention; and

FIG. 3 is a schematic illustration of a telecommunications system,according to an embodiment of the present invention;

FIG. 4 is a schematic illustration of coverage areas of the LA-cell anda plurality of SA-cells in a telecommunications network, according toone embodiment of the present invention;

FIG. 5 sets forth a flow diagram of method steps for selecting one ormore SA-cells when the terminal measures signals from the SA-cells,according to one embodiment of the present invention;

FIG. 6 sets forth a flow diagram of method steps for selecting one ormore SA-cells when the terminal transmits an information requestmessage, according to one embodiment of the present invention; and

FIG. 7 sets forth a flow diagram of method steps for selecting one ormore SA-cells when the terminal transmits an information requestmessage, according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

A description of example embodiments of the invention follows.

The teachings of all patents, published applications and referencescited herein are incorporated by reference in their entirety.

FIG. 3 illustrates a telecommunication system 10 ac-cording to oneembodiment of the present invention. As shown, the telecommunicationsystem 10, which is preferably a cellular wireless accesstelecommunication system, includes at least a decision unit 11, anLA-cell 12, and SA-cells 13 and 14. FIG. 3 also illustrates a userterminal 15. For clarity reasons, only the most relevant elements of thetelecommunication system are illustrated in FIG. 3. Other elements, notshown in FIG. 3, may also be present and are within the scope of thepresent invention. Such “other elements” may include e.g. additionalSA-cells, additional LA-cells, additional terminals, further elements tothe telecommunication system and the backhaul links connecting each cellwith the telecommunication system and/or with each other.

Below, a general description of each of the decision unit 11, theLA-cell 12, the SA-cells 13, 14, and the terminal 15 is provided. A moredetailed description of the functionality of each of these elements isprovided in the discussion of the different solutions, following thegeneral description.

The decision unit 11 is a unit which may exchange messages with at leastthe terminal 15 and, possibly, with the SA-cells 13,14. In someembodiments, as described in greater detail below, the decision unit 11may be configured to select one or more SA-cells with which the terminal15 may establish a data connection. To that end, in one embodiment, thedecision unit 11 may include at least a communications interface forexchanging messages, a memory for storing data (possibly received in themessages) and/or computer program instructions, and a processor forprocessing data, running computer programs, etc. In other embodiments,the decision unit 11 may be implemented in software or in firmware. Inyet other embodiments, the decision unit 11 may be implemented as anycombination of hardware, software, and firmware.

In the illustrative embodiment of FIG. 3 the decision unit 11 is shownto be a part of the LA-cell 12. However, in other embodiments, thedecision unit 11 may be not included in the LA-cell 12, but be astand-alone unit, be included in a further network node, or bedistributed between two or more network nodes (e.g. a part of thefunctionality of the decision unit 11 may be implemented within theLA-cell 12, while another part may be implemented in a further networknode, not shown in FIG. 3). Unless indicated otherwise, discussionsprovided herein with respect to the decision unit 11 apply both to theembodiments where the decision unit 11 is a part of the LA-cell 12 andwhere the decision unit 11 is implemented outside of the LA-cell 12.

The LA-cell 12 is an LA-cell cell configured to at least be able toenable terminal 15 to camp on LA-cell 12 and to page the terminal 15 ina conventional manner known in the art. According to some embodiments ofthe present invention, the LA-cell 12 is also configured to receiveservice request messages (SRMs) from the terminal 15 indicating that adata connection needs to be established between the terminal 15 and oneof the SA-cells for supporting wireless traffic (i.e. wireless exchangeof user data), not shown in FIG. 3. While the LA-cell 12 is notprimarily intended to be used to carry wireless user data from/to theterminal 15, it is not precluded that other signalling than paging orthat also some user data traffic is carried via the LA-cell 12, forexample low bit rate traffic (such as a voice call) for the fullduration or for a part of the duration of the data session (call).

In comparison with the SA-cells 13 and 14, the LA-cell 12 is configuredto cover a larger geographical area with a smaller bit rate. Thegeographical area where an idle terminal selects the LA-cell to camp onis referred to as the coverage area of the LA-cell. In a properlydimensioned cell, a terminal within that area is usually also capable ofsuccessfully receiving the system information and signalling messagesfrom the LA-cell (for example a paging message). This is assumed to alsoapply in the reverse direction, i.e. when a terminal, camping on anLA-cell, transmits a signalling message (for example a service requestmessage) to the LA-cell it is camping on, the LA-cell is usually capableof successfully receiving the message. In the intended coverage area ofthe wireless access network it may be assumed that at least one LA-cell(in FIG. 3, the LA-cell 12) is fully operational or ‘normally on’ and iscapable of supporting exchange of signalling messages with theterminals. In a simplest embodiment, this may mean that the LA-cell 12is always fully functional (‘on’). In other embodiments, power-savingoptions suitable for LA-cells may be applied to the LA-cell 12, meaningthat the LA-cell 12 would not necessarily always be ‘on’.

The terminal 15 may be a terminal operated by an actual human user, suchas e.g. a mobile phone with which the user can make a voice call orbrowse the Internet, but may also be a smart phone or a blackberryoperating without human intervention (e.g. sending/receiving e mail),and may also be an M2M device, such as e.g. a smart electricity meter ora camera surveillance device.

The terminal 15 may be in an active mode or in an idle mode. As usedherein, the terminal 15 is said to be in an idle mode while there is nosupport for a wireless exchange of user data or traffic between theterminal 15 and the SA-cells 13 or 14. As used herein, the terminal 15is said to be in an active mode when it is able to exchange data with atleast one of the SA-cells 13, 14. Note that while these notions of idlemode and active mode may be comparable with the meaning of like terms instandardized conventional networks, as used herein, they do notnecessarily coincide exactly with such standardized definitions.

Further, the terminal 15 may support some form of power-saving options(i.e., be in a power-save mode or in an operational mode, where theterminal consumes less power in the power-save mode than in theoperational mode). Since the differentiation between power-save andoperational modes is based on the amount of power consumed by theterminal, while the differentiation between idle and active modes isbased on the presence of the support for wireless exchange of user datawith the SA-cells, a terminal may e.g. be in the operational mode butstill be an idle terminal (or the terminal in the operational mode maybe in active mode). Similarly, a terminal in a power-save mode can beeither active or idle, depending on whether the terminal supportswireless exchange of user data with at least one of the SA-cells. Mostcommon, however, would be a situation where an idle terminal in apower-save mode “wakes up” (i.e. exits the power-save mode and entersthe operational mode) to perform certain actions to facilitateestablishment of a data connection with at least one SA-cell, afterwhich the terminal becomes “active” (and operational). Since theembodiments of the present invention deal with a session setup for theterminal (i.e. establishment of a data connection with one or moreSA-cells), in the following description, the differentiation is mainlymade between idle and active modes of the terminal.

The terminal 15 in an idle mode may be assumed to ‘camp’ on at least theLA-cell 12, which may also be realized in a conventional manner. Forexample, the LA-cells may broadcast a pilot signal or a beacon signalwhich can be received by the terminal 15 which then uses the informationcontained in the received signal to select or re-select the LA-cell tocamp on. In FIG. 3, the signals transmitted by LA-cell 12 and receivedby the terminal 15 are illustrated as a solid arrow. In an embodiment,the terminal 15 may be capable of informing the network about the changeof location/routing area in order to facilitate the paging function ofthe LA-cell 12, not shown in FIG. 3.

The SA-cells 13 and 14 are data cells, primarily in-tended to carry userdata traffic from/to the terminal 15 over the data connectionsestablished for that purpose. However, it is not precluded that alsosome other information and/or some signalling is carried via one or moreof the SA-cells.

Each of the SA-cells 13 and 14 are intended to be capable of coveringsmaller areas with a higher bit rate, as opposed to the LA-cell 12. In atypical deployment scenario, the areas that can possibly be covered bynearby SA-cells may show a considerable overlap. In the intendedcoverage area of the wireless access network it may be assumed that atleast one of the SA-cells 13, 14 is able to provide coverage. An SA-cellis only fully operational when and to the extent that it is needed or,in other words, is ‘normally off’. An SA-cell is assumed to support atleast one form of power-saving, e.g. a power-save mode or stand-by mode.To that end, an exemplary embodiment of FIG. 3 illustrates that theSA-cell 13 is an SA-cell in a power-save mode (indicated in FIG. 3 as awhite triangle), while the SA-cell 14 is an SA-cell in an active mode(indicated in FIG. 3 as a dark triangle). In FIG. 3, the signalstransmitted by active SA-cell 14 and received by the terminal 15 areillustrated as a solid arrow, while a possible signal transmitted bySA-cell 13, which is in power-save mode, and received by the terminal 15is illustrated as a dashed arrow.

Each of the terminal 15, the LA-cell 12, and the SA-cells 13, 14 mayinclude at least one or more of a processor, a memory unit, and acommunications interface configured for carrying out functionalities ofthese units described herein.

FIG. 4 is a schematic illustration of coverage areas of an LA-cell and aplurality of SA-cells in a telecommunications network, according to oneembodiment of the present invention. As shown in FIG. 4, an LA-cell 22,which could be the LA-cell 12 illustrated in FIG. 3, may have arelatively large coverage area, shown with a dashed circle 23. Each ofthe plurality of SA-cells, shown as triangles, such as the triangles 24,could be the SA-cells 13, 14 illustrated in FIG. 3. The SA-cells 24 mayhave different, relatively smaller coverage areas, shown with solidcircles, such as circles 25. FIG. 4 further illustrates idle modeterminals 26 and active mode terminals 27 (the active mode terminalsindicated as bold outlined terminals). Each of the terminals 26 and 27could be the terminal 15 illustrated in FIG. 3 and could be within oneor more of the coverage areas 25. The idle mode terminals 26 within thecoverage area 23 of the LA-cell 22 are said to be camping on the LA-cell22. The SA-cells 24 having coverage areas 25 shown in white are intendedto illustrate the SA-cells in the power-save mode, while the SA-cells 24having coverage areas 25 shown in dark grey are intended to illustratethe SA-cells in the active mode and have ongoing data sessions with oneor more active terminals 27. Of course, in other embodiments, thecoverage areas 23 and 25 do not have to be circular.

Solution #1: Session Setup Via the Terminal in Idle Mode MeasuringSignals Transmitted by Sa-Cells

In the context as illustrated in FIGS. 3 and 4 and described above, theterminal 15 is first assumed to be an idle terminal which intends tobecome active, either because it receives a page (e.g. from the LA-cellthe terminal camps on, e.g. the LA-cell 12) or because the terminal 15(possibly via the user of the terminal or via an application running onthe terminal) indicates the desire to exchange user data. Embodiments ofthe present invention address the problem of selecting (assigning) asuitable SA-cell (one already active or one currently in power-savemode) for that terminal.

For reference, in a conventional network, the terminal would initiateactive mode via the cell that it is currently camping on (and, whenapplicable, via which the terminal received a page) and also theresulting data connection for carrying user data traffic is supported bythe same cell (not excluding a handover or directed retry to a differentcell). In contrast, the following provides solutions for anenergy-efficient network as illustrated in FIG. 3 where signalingmessages between the terminal and the network are exchanged using theLA-cell, but a data connection for exchanging user data is establishedwith one of the SA-cells.

Embodiments of this solution are based on the idea that at least some ofthe SA-cells in a telecommunications network are configured to emitsignals which the terminal 15 is able to receive while the terminal isin the idle mode. While still in the idle mode and camping on theLA-cell 12, the terminal 15 is further configured to analyze thereceived signals. More specifically, the terminal 15 in the idle mode isconfigured to determine properties representing propagation conditionsof the received signals, such as e.g. a signal strength and/or a pathloss estimate for the signal. The terminal 15 is also configured toprovide a report to the decision unit 11, via the LA-cell 12, containingat least the information regarding at least some of the determinedproperties for at least some of the SA-cells for which the terminal 15received and analyzed the signals. Based, at least partially, on theinformation contained in the report received from the terminal 15, thedecision unit 11 is then able to make a selection of at least one of theSA-cells in the tele-communications network to serve the terminal 15. Inother words, the decision unit 11 is able to select one or more SA-cellswith which the terminal 15 could establish the data connection forexchanging user data.

In this manner, the terminal 15 facilitates establishment of the dataconnection between the terminal 15 and one of the SA-cells by providingto the decision unit 11 information regarding the propagation conditionsbetween the terminal 15 and various SA-cells. When the decision unit 11has such information available, a selection of the most appropriateSA-cell for establishing the data connection may be performed quickerand/or more accurately.

FIG. 5 sets forth a flow diagram of method steps for selecting one ormore SA-cells when the terminal 15 measures signals from the SA-cells,according to one embodiment of the present invention. While the methodsteps are described in conjunction with FIG. 3, persons skilled in theart will recognize that any system configured to perform the methodsteps, in any order, is within the scope of the present invention.

The method begins in step 31, where one or more SA-cells in the networktransmit signals intended for the terminal 15. In step 32, the terminal15 is configured to receive and process at least some of the signalstransmitted by the SA-cells.

According to the embodiments of the present invention, not only activeSA-cells may emit signals that the terminal 15 may receive and analyze,but also SA-cells in a power-save mode. The latter is particularlyadvantageous for energy-efficient networks because transmitting signals(e.g. pilot and system information) can amount to a substantial portionof the cell's maximum transmit power, such that a cell without anytraffic or a cell carrying little traffic is very energy-inefficient.However, according to some embodiments of the present invention, anSA-cell in a power-save mode may also be configured to emit a signalthat the terminal 15 can receive and analyze. To that end, the SA-cellin a power-save mode may be configured to only emit a so-called“presence signal,” e.g. a signal emitted intermittently, for a fractionof the time. For example, such a SA-cell may be configured to emit thesignal for 1 second, followed by 9 seconds of not emitting the signal,corresponding to a fraction 1/10th. Varying the duty cycle (i.e. theratio between the “on” and “on”+“off” times for emitting the signal) inthis manner allows reducing the power of the emitted presence signal toroughly the same fraction, as opposed to a conventional approach where atransmission would be substantially 100% of the time. In one embodiment,the maximum duty cycle for an intermittent signal emitted by an SA-cellcould be e.g. ⅛th, which could result in an 8-fold power saving incomparison with the same signal emitted continuously.

The signals emitted by the SA-cells should be suitable for the terminal15 in an idle mode to detect and analyze. This means that the signalsshould be lasting sufficiently long and should be decodable by theterminal. The signals should preferably be sufficiently frequent toallow the terminal 15 to receive and analyze the intermittent signalwithout excessive waiting time, should be emitted e.g. once per second.

In addition, the signals should be such that the terminal candifferentiate between the signals received from the different SA-cells.In one embodiment, the differentiation may be done by each SA-cellemitting a signal that is uniquely coded. In another embodiment, eachSA-cell may include its identification in the signal. In yet anotherembodiment, each SA-cell may emit signals via a different channel andthe terminal 15 may be configured to “listen” to these differentchannels. Further, if the SA-cells emit their signals intermittently,the terminal 15 may also differentiate between the SA-cells based on thetime the signal is received (provided that there is synchronizationbetween the terminal and the SA-cells and the terminal has access toinformation indicative of the times when the signals from eachrespective SA-cells should be expected to be received). Of course, acombination of these embodiments and other manners for differentiatingbetween the signals received from different SA-cells are also possibleand within the scope of the present invention.

In one embodiment, identification of the SA-cell provided in any one ofthe manners described above could be a globally unique identificationwhich allows global differentiation between each SA-cell. However, sucha globally unique identification is not always necessary. In otherembodiments, the identification may be such that it uniquely identifiesa particular SA-cell in e.g. a particular, relevant geographical area(e.g. the SA-cell which provides at least partial coverage in thecoverage area of the LA-cell).

In an embodiment particularly useful for the SA-cells in power-savemode, the transmission of the signals by the SA-cells may be configuredto take place in a predetermined pattern (e.g. periodically). An idleterminal in a power-save mode may then be configured to synchronize its“wake-up” times for receiving and analyzing the signals of at least themost relevant of these SA-cells.

With a predetermined transmission pattern of the SA-cells, it may be anoption to organize the transmission instances of the presence signals ofthe SA-cells (at least the ones of particular relevance to the terminal,e.g. those in the vicinity of each other) such that these transmissions,as far as possible, do not consistently coincide. This may be beneficialfor several reasons. One reason is that it may enable the terminal tomore easily differentiate between the signals received from thedifferent SA-cells. Another reason is that it may allow the terminal tomake assessments of several SA-cell presence signals in a quicksuccession, e.g. one SA-cell at the time, and without interference frompresence signals of other SA-cells nearby the terminal (possibly withreceived signal strengths in the same range as from the first SA-cell).

An alternative option for the predetermined transmission pattern of theSA-cells could be to organize the transmission instances of the presencesignals of the SA-cells so that the transmissions would substantiallycoincide. This option is viable if a terminal is able to performmeasurements on several SA-cell presence signals at the same time, whichrequires more processing power in the terminal. This would allow theterminal to make several SA-cell presence signal assessments at a timeand then go back to the power-save mode again.

In one embodiment, an idle terminal in a power-save mode may exit thepower-save mode at some predetermined times in order to receive andmeasure the signals from the SA-cells. The terminal may do so e.g.periodically or upon receiving a paging signal from the LA-cellindicating to the terminal that, for example, a data connection needs tobe established or that a report is requested for e.g. network managementpurposes and/or for terminal localization. In another embodiment, anidle terminal may be configured to only start monitoring the signalsfrom the SA-cells when the terminal needs to establish a dataconnection. Such an embodiment would allow saving power during the timewhen the terminal is in idle mode, but may result in increased latencybefore the terminal is able to transmit the relevant information to thedecision unit, thus increasing the latency in establishing the dataconnection. For many applications, e.g. checking and retrieving new emails, such an increase in latency would have no significant effect onthe application.

In yet another embodiment, one or more of the SA-cells in a power-savemode may be triggered by the LA-cell to emit the signal to be receivedby the terminal. This may be done in response to e.g. the LA-cellreceiving a service request message from the terminal or when (orbefore) the LA-cell pages the terminal. If the terminal is also in apower-save mode, the LA-cell could synchronize the trigger for theSA-cells to transmit the signals with a trigger for the terminal toreceive and analyze the signals. This embodiment also holds for the oneor more SA-cells in a power-save mode being triggered by the decisionunit 11, which could either be a part of the LA-cell 12 or be an entityoutside of the LA-cell 12.

A trigger for the SA-cells to transmit the signals could be based, atleast partially, on one or more of a terminal location estimate, anestimate of the accuracy of the terminal location estimate, and activitystatus of the SA-cells in the vicinity of the estimated terminallocation. In one embodiment, the terminal location estimate and theestimate of the accuracy of the location estimate could be provided tothe LA-cell by the terminal because the terminal has a built-in GPSreceiver which is typically able to provide both a position estimate andan indication of the accuracy of the position estimate. In anotherembodiment, these values may be derived by the LA-cell from the contentsof a service request message received from the terminal. This may bedone e.g. by the terminal providing signal levels of all kinds ofsignals received (e.g. active SA-cell signals, WiFi hotspot signals,LA-cell signals, etc.) The LA-cell (or a separate location estimatingunit associated with the LA-cell) may then process this information intoa position estimate and an accuracy estimate.

The terminal 15 may be configured to maintain a list of at least themost recent and most relevant results for the measured signals togetherwith the indication of the corresponding SA-cells.

In step 33, the terminal 15 is configured to provide a report to thedecision unit 11 regarding at least some of the determined propertiesthe SA-cells that the terminal analyzed. The terminal 15 may beconfigured to provide the report to the decision unit 11 via the LA-cell12. Such an embodiment may be advantageous because the LA-cell may beconfigured to add information to the report passed to the decision unit,such as e.g. an identification of the LA-cell. In addition, the decisionunit 11 having the identification of the LA-cell may further facilitateidentification of the SA-cells about which the report containsinformation.

In one embodiment, the terminal 15 may provide the report periodically,even when there is no immediate need for establishing the dataconnection. Such an embodiment has the advantage that the decision unit11 may have sufficient information available for selecting the mostappropriate SA-cell to serve the terminal when the data connection doesneed to be established. It may also provide the network with moreaccurate information about the terminal location than just thelocation/routing area, which information may be relevant for e.g.statistical purposes.

In another embodiment, the terminal 15 may only provide the report uponreceiving a paging signal from the LA-cell or when the terminal wants tobecome active (i.e. when a data connection needs to be established). Inthe latter case, the terminal may be configured to send a servicerequest message (SRM) to the network via the LA-cell and may include thereport in the SRM. Thus, the report is then provided to the decisionunit as a part of a connection setup procedure.

As previously described, the report includes at least informationregarding at least some of the determined properties for at least someof the SA-cells for which the terminal 15 received and analyzed thesignals. In other words, out of all of the SA-cells in thetelecommunications network (or at least the plurality of the SA-cells inthe vicinity of the terminal), the terminal may receive signals fromonly some of these cells. The terminal may then analyze not all of thereceived signals, but only some of those (e.g. because some signals maybe impossible to analyze or because they may be associated with theSA-cells that the terminal is not interested in establishing a dataconnection with). Further, the terminal may decide to include in thereport not all of the information regarding the propagation conditionsfor all of the analyzed SA-cells, but only the information for some ofthe analyzed SA-cells and/or only part of the determined information.For example, the terminal may decide to not include the signal strengthsfor the most relevant SA-cells, but to include the determined path lossestimates, e.g. because the path loss is considered to be more relevantto the decision unit and/or to limit the size of the report and/or whenresults for many SA-cells have been determined.

In one embodiment, the report may also include one or more of thefollowing: an identification of each SA-cell for which information isprovided, identifications of the SA-cells for which the signals werereceived but for which the information is not provided in the report, anindication of which SA-cells are active and which are in a power-savemode, and a 1 bit flag indicating that there is no coverage provided bya particular SA-cell at the location where the service is requested.

If the report is received by the decision unit 11 when a data connectionneeds to be established (i.e. when the terminal has been paged or theterminal indicates a desire to establish a data connection), thedecision unit 11 then may proceed, in step 34, to use at least some ofthe information provided in the report to select one or more SA-cellswith which the terminal may establish the data connection. For example,in one embodiment, the decision unit 11 may take into consideration pathloss estimates provided in the report and select the SA-cell with thelowest path loss estimate (e.g. the SA-cell closest to the terminal) asthe cell for serving the terminal. The decision unit 11 may, however,also take other information into consideration when making theselection, such as e.g. power and/or load considerations on thecandidate SA-cells, capabilities of the SA-cells and the terminal(including e.g. the supported RATs), the type of the required service,and the urgency of establishing the data connection (i.e., whetherestablishing the service is time-critical or not). For example, the mostsuitable SA-cell for the terminal could be not necessarily the SA-cellwith the lowest path loss to the terminal because it may be moresuitable to keep the closest SA-cell in a power-save mode (theindication of which could be provided in the report) and to select adifferent, e.g. already active, SA-cell for serving the terminal. Inanother example, it could be that the closest SA-cell is already heavilyloaded and that a different, more distant, SA-cell is more suitable. Inyet another example, it could be that the closest SA-cell supports aless energy-efficient RAT than a different, more distant, SA-cell. Inyet one more example it could be that the SA-cell indicated in thereport as having the highest signal strength and/or the lowest path lossestimate does not have the capabilities for carrying a particularservice and, therefore, the “next best” SA-cell is selected from theones provided in the report that does have the required capabilities.Alternatively, after evaluating the report, the decision unit 11 maydecide that none of the SA-cells are suitable for carrying the service(this may particularly be the case for time-critical services and/orwhen the 1 bit flag(s) in the report indicates that there currently isno coverage by any SA-cell at the location where the service isrequested) and that the LA-cell instead should serve the session,possibly with a reduced bit rate and/or possibly only temporarily, e.g.until a suitable SA-cell becomes available.

If there is no need to establish the data connection at the time whenthe report is received, the decision unit 11 may be configured to storethe report for later use and evaluation. Alternatively, the decisionunit may still go through the process of selecting one or more SA-cellsthat could serve the terminal in case there is a need to establish adata connection and store that information, possibly along with thereport.

Once one or more SA-cells are selected by the decision unit 11 as themost appropriate SA-cells for establishing the data connection with theterminal, the decision unit 11 may indicate the selected SA-cells to theterminal. In one embodiment, such indication may be provided via theLA-cell (e.g. in response to receiving a SRM received from the terminalvia the LA-cell). In this embodiment, the decision unit 11 may providean indication also to the selected SA-cells to inform these SA-cellsthat a session set up is to be expected. In another embodiment, suchindication may be provided via one or more of the selected SA-cells. Thelatter embodiment assumes that a channel (with mutually known resourcedetails) between the terminal and the selected SA-cell can be madeavailable, along which channel an SA-cell may initiate the set up of adata connection to the terminal. In both these embodiments, the selectedSA-cell(s) may be provided with further information related to theterminal and/or the subscription (such as, for example, data connectionparameters and/or authentication information and/or encryption keys) inorder to facilitate a more speedy session set up. This information maybe supplied by the decision unit and/or may be requested by the decisionunit to be supplied from a data base (such as the HLR/VLR (Home LocationRegister/Visitor Location Register) to the selected SA-cells.

If any of the selected SA-cells are in a power-save mode, the decisionunit 11 may further be configured to activate the selected SA-cells(possibly via the LA-cell).

The terminal 15 may further be configured for establishing the dataconnection (i.e., setting up a traffic channel) with the selected one ormore SA-cell. Further, a route for the traffic (and the associatedsignaling) may be set up connecting the selected SA-cell(s) and thenetwork.

Once the decision unit 11 knows the identities of the selected SA-cells,the decision unit 11 may assist in and prepare for setting up the routefor the traffic connecting the selected SA-cells and the network. Thismay also be performed by LA-cell 12 when decision unit 11 is within theLA-cell or when the decision unit provides the information to theLA-cell.

In a cellular wireless telecommunication system it may happen that aterminal in active mode, having a connection with a particular cell,moves out of (the coverage area of) that cell and into (the coveragearea of) another cell. Then a so-called handover (handoff) may beperformed, meaning that the connection between the terminal and thecurrent cell (source cell) is transferred (handed over) to a connectionbetween the terminal and a different cell (target cell).

Solution #1 as described above may also be used in an energy-efficientwireless network to facilitate a handover of the data connection betweenan active terminal and the SA-cell it has established the dataconnection with to another, different, SA-cell.

An active terminal may perform measurements on signals received fromvarious SA-cells as described above, e.g. periodically and/or when thesignal received from the SA-cell it has established a data connectionwith drops below a predetermined threshold and/or when triggered by thenetwork. The terminal may then provide the report to the decision unitvia the LA-cell. The decision unit may evaluate the informationcontained in the report received from the terminal and, taking intoaccount considerations similar to the ones described above, select adifferent SA-cell as target SA-cell for a handover.

As described above, the decision unit may further inform the terminaland/or the LA-cell and/or the involved (source and target) SA-cells.

Solution #2: Session Setup Via Sa-Cells Measuring Signal Transmitted bythe Terminal in Idle Mode and the Terminal Selecting the Sa-Cell Basedon the Measurements

Similar to the solution #1 described above, in the context asillustrated in FIGS. 3 and 4, the terminal 15 is assumed to be an idleterminal which may, in the future, have to transfer to an active mode,either because it receives a page (e.g. from the LA-cell the terminalcamps on, e.g. the LA-cell 12) or because the terminal 15 (possibly viathe user of the terminal) initiates exchange of user data. Similar tothe solution #1, embodiments of the solution #2 also address the problemof selecting (assigning) a suitable SA-cell (one already active or onecurrently in power-save mode) for that terminal.

Embodiments of solution #2 are based on the idea that a terminal in theidle mode is configured to emit a signal, referred to herein as aninformation request message (IRM), intended to be received by one ofmore of the SA-cells in the telecommunications network. In some ways,the IRM may be comparable to the SRM, described above, that the terminal15 transmits to the LA-cell when the terminal wishes to initiate a setupof the signaling connection with the LA-cell. The IRM is used to havethe SA-cells receiving the IRM to perform measurements on the receivedsignal, e.g. to determine the strength with which the signal wasreceived. Similar to the SRM, the IRM may also be used by the terminalto indicate that the terminal wishes to establish a connection and,optionally, to include parameters indicative of the requested connectionand/or of the terminal's capabilities. Unlike the SRM, the IRM isintended to be received by the SA-cells and is intended to indicate tothe SA-cells that the terminal may need to setup a data connection withat least one of them.

Preferably, the IRM is transmitted such that it may be easily receivedand decoded by an SA-cell, even more preferably also when the SA-cell isin power-save mode. The IRM may be transmitted on a particular separateradio interface which is different from any of the RATs the terminal iscapable of employing for supporting signaling and/or data connections.However, it is not precluded that the IRM is transmitted using a RAT theterminal is capable of employing for supporting a signaling connectionand/or a data connection, for example the LA-cell's RAT the terminal iscamping on (in which case different frequencies and/or different codescould be used, as known in the art). The transmission of the IRM furtherdiffers from the SRM in that the SRM is directed to and addressed to aparticular cell (i.e. the LA-cell that the terminal identified and iscurrently camping on) and has a purpose to e.g. establish a signalingconnection with that particular cell. In contrast, the IRM is notdirected to nor addressed to any particular cell (the IRM is broadcast)and has a purpose to e.g. identify one or more cells (SA-cells).

At least some of the SA-cells in the telecommunication system may beable to receive the IRM transmitted by the terminal and determine thesignal strength with which they received the IRM. At least some of thoseSA-cells that determined the signal strength of the received IRM canthen provide messages to the terminal indicating the determinedstrength. At least partially based on such messages received from theSA-cells, the terminal can then make a selection of one or more of themost appropriate SA-cells for establishing the data connection with.

In this manner, the terminal 15 facilitates establishment of the dataconnection between the terminal 15 and one of the SA-cells by firstenabling the SA-cells to obtain information indicative of thepropagation conditions between the terminal 15 and various SA-cells(e.g., signal strength) and then collecting the obtained informationfrom the SA-cells in order to select an appropriate SA-cell forestablishing the data connection. As a result, establishment of the dataconnection may be performed quicker and/or more accurately.

FIG. 6 sets forth a flow diagram of method steps for selecting one ormore of the SA-cells 13, 14 when the terminal 15 transmits aninformation request message, according to one embodiment of the presentinvention. While the method steps are described in conjunction with FIG.3, persons skilled in the art will recognize that any system configuredto perform the method steps, in any order, is within the scope of thepresent invention.

The method begins in step 41 where the terminal 15 in an idle modetransmits an IRM. In one embodiment, the terminal 15 may be configuredto transmit the IRM at some predetermined times and/or at somepredetermined pattern, even though there is no immediate need toestablish a data connection with any of the SA-cells. In otherembodiments, the terminal 15 may be configured to transmit the IRM whenthe terminal receives an indication that the data connection between theterminal and one of the SA-cells should be established. Such anindication could e.g. be a paging message received from the LA-cell 12on which the idle terminal 15 is camping or be an indication from theuser of the terminal or an application running on the terminal wishingto exchange user data over the established data connection.

In one embodiment, the IRM may be transmitted via a broadcast channel.The IRM is not intended for and not directed towards the LA-cell (asopposed to e.g. a service request message typically used in conventionalnetworks) but is intended for SA-cells which may potentially provideservice to the terminal 15. To that end, the IRM could also includeinformation indicative of the request of the terminal for establishing adata connection between the terminal and one of the SA-cells.

The IRM may include at least some means that would enable the SA-cellsreceiving the message to identify the terminal that sent it so that theSA-cells can differentiate between the IRMs received from differentterminals. In one embodiment, the differentiation may be done by theterminal including its (possibly partial) identification in the IRM.Instead of or in addition to a direct identification of the terminal(such as the full or partial terminal ID), the terminal may include akind of reference (tag or label) in the IRM. Such a reference may enablethe SA-cell to discriminate between IRMs received from differentterminals. Further, the SA-cell may include (e.g. copy) the receivedreference (tag or label) in the response message, thus also enabling theterminal to discriminate between response messages relating its own IRMand those that might be received but relate to IRMs transmitted bydifferent terminals. Selecting a randomized number as reference (tag orlabel) for the IRM may serve this purpose.

The (partial) identification may e.g. be coded in the contents of theIRM and/or may be coded by transmitting the IRM on one or more ofmultiple frequencies and/or by transmitting the IRM with one or more ofmultiple channel codes. In another embodiment, the differentiation maybe done by the terminal transmitting the IRM at a particular time, forexample in one or more of multiple time slots which time slots may berepeated in a predetermined pattern, e.g. periodically. The SA-cell canthen differentiate between the terminals based on the times or timewindows the IRMs are received (provided that there is synchronizationbetween the terminal and the SA-cells). Of course, a combination ofthese embodiments and other manners for differentiating between thesignals received from different terminals are also possible and withinthe scope of the present invention.

In one embodiment, identification of the terminal provided in any one ofthe manners described above could be a globally unique identificationwhich allows global differentiation between each terminal. However, sucha globally unique identification is not always necessary. In otherembodiments, the identification may be such that it uniquely identifiesa particular terminal in e.g. a particular, relevant geographical area(e.g. the terminal in the coverage area of the SA-cell).

In yet another embodiment, the terminal may be configured to include inthe IRM an identification of the network to which the terminal belongs.By providing such identification in the IRM, the SA-cell receiving theIRM can differentiate between the IRMs received from terminals belongingto different networks and then choose whether or not to respond. Forexample, the SA-cell may choose not to respond when the IRM is sent by aterminal in a competitor's network. In this case, the providedidentification does not need to be terminal-specific. It would besufficient to only identify the network that the terminal belong to.

The IRM may also include an indication of access priority. For example,an emergency response terminal or a consumer terminal making anemergency call may include an indication of high access priority or anM2M terminal (e.g. electricity meter) may include an indication of lowaccess priority. By providing such an indication in the IRM, the SA-cellreceiving the IRM can differentiate between the IRMs received fromterminals and/or purposes having different access priorities and thenchoose whether or not to respond.

Further, the IRM should be such as to allow the receiving SA-cell todetermine the signal strength with which the IRM is received and/or toestimate the path loss between the terminal and the receiving SA-cell.

Optionally, the IRM may include an indication of the service(s)requested and/or the terminal capabilities, which may be relevant to aSA-cell receiving the IRM in determining to what extent the SA-cell iscapable and able to provide the requested service. The terminalcapabilities that could be identified in the IRM include e.g. one ormore of supported frequency band(s), supported RAT(s), supportedmode(s), power with which the IRM is sent by the terminal, supported(maximum) terminal power, and requested (minimum) bit rate.

In one embodiment, the terminal 15 may transmit the IRM with arelatively high power in order to maximize the likelihood that at leastone suitable SA-cell is able to detect the IRM. In one furtherembodiment, the terminal may transmit the IRM at the maximum terminal'stransmitting power. In an alternative embodiment, the terminal 15 maydecide to transmit the IRM at still relatively high power, but at lessthan the maximum transmitting power. This could be sufficient if, forexample, the terminal already has measured signals from at least onesuitable active SA-cell and, therefore, there is no need to transmit theIRM with more power than to overcome the path loss to the best currentlyactive SA-cell. Such an IRM would only need to reach the SA-cell(s) inpower-saving mode that could possibly be better candidate(s) than thebest currently active SA-cell. Another example of transmitting the IRMat less than the maximum terminal's transmitting power could be that thesystem information provided by a currently active SA-cell or by theserving LA-cell also includes information about the SA-cell density inthe area. In such an example, the terminal may limit the transmittingpower for the IRM accordingly.

In an embodiment, the terminal 15 may be configured to transmit the IRMmore than once, in a sequence, e.g. to overcome the possibility ofcorruption by noise, to overcome the possibility of interference from asimilar message from a different terminal, and/or to overcome the sleepperiod of an SA-cell in power-save mode and listening for only afraction of the time. In such an embodiment, the terminal may beconfigured to transmit subsequent IRMs in the sequence with increased orwith increasing power. The terminal may also be further configured totransmit subsequent IRMs with a randomized delay relative to thepreceding IRM in the same sequence, in order to avoid subsequentcollisions of the IRMs.

In step 42, at least some of the SA-cells may receive the IRMtransmitted by the terminal and process the IRM by at least determiningthe signal strength with which the IRM is received. The SA-cells mayfurther be configured to estimate the path loss from the terminal to thereceiving SA-cell. The SA-cell may use the estimated path loss for e.g.estimating whether a requested (minimum) bit rate is at all feasible onthe wireless path between the terminal and the SA-cell (and, if not, theSA-cell may decide to refrain from responding).

The SA-cell may be configured to process all of the IRMs that itreceives or may choose to ignore some IRMs, such as those requesting aservice that the SA-cell is unable to deliver at the moment (e.g.because an unsupported RAT and/or frequency band is requested, and/orbecause the SA-cell is already highly loaded), and/or those IRMs thathave been received with a low signal level and/or with a high estimatedpath loss. The SA-cell may also be configured to ignore IRMs receivedfrom the terminals not related to the network of the SA-cell (e.g.terminals related to a competitor's network) and/or to ignore IRMsreceived with an access priority indication lower than a predeterminedthreshold. The SA-cell may be able to identify a terminal as belongingto a different network based on the terminal identification provided inthe IRM (for such an embodiment, the identification does not need to beterminal-specific, a network-specific identification is sufficient).

It may be noted that, in various embodiments, a wireless access networkmay contain multiple different types of SA-cells, e.g. SA-cellssupporting different (or multiple) frequency bands, SA-cells supportingdifferent (or multiple) RATs, SA-cells supporting different (ormultiple) modes of operation, and/or SA-cells of different sizes(macro-, micro, pico- and femtocells). Still, each of these SA-cells maybe configured to have an SA-cell's monitoring of IRMs which could beperformed regardless the SA-cell's specific capabilities for the datatransfer (data connection or traffic channel). In fact, the radiointerface at the terminal for transmitting the IRM and the radiointerface at the SA-cells for receiving the IRMs may be designedspecifically for the IRMs and may be independent of the SA-cell'scapabilities for data transfer (data connection or traffic channel).However, in case the frequencies used for the communicating the IRMs andfor communicating the actual user data over the established dataconnection would be significantly different, then the signal strengthmeasurement and/or path loss estimate made using the frequency at whichthe IRM was sent may be not very well representative for the path losson the frequency to be used for the actual user data transfer (e.g. whenthe IRM is transmitted in the 900 MHz range while the data connection isestablished in the 5 GHz range). In such cases, a similar IRM may bedefined using a different frequency (e.g. in the 3 GHz range) thatallows a more representative signal strength/path loss estimate. Theterminal 15 may then be configured to transmit either or both of theseIRMs, even simultaneously, if needed.

At least the SA-cells in the power-save mode may be configured tomonitor (listen) for the IRMs which may be emitted by the terminals. TheSA-cells in the active mode may also be configured to listen for theIRMs, however such listening by the active SA-cells may be not requiredwhen the terminal is configured to monitor the signals of the activeSA-cells serving one or more other terminals and when the signalsreceived by the terminal enable the terminal to sufficiently assess thesuitability of these candidate SA-cells. Then, the terminal may maintaina list of suitable active candidate SA-cells for establishing the dataconnection.

In an embodiment, the SA-cells in the power-save mode can be configuredto enter the listening mode (i.e. be capable of receiving IRMs) only fora fraction of time, in order to limit power consumption. For example,the SA-cell in the power-save mode may enter the listening modeperiodically, for e.g. 1/10th of the time, thus reducing the powerconsumed for this purpose to roughly the same fraction (compared to thesituation with listening for 100% of the time). In such embodiments, thelistening periodicity, the duration of the IRMs transmitted by theterminal, and/or the number of repetitions of the IRMs in a sequencecould be selected such that at least one IRM can be received within aSA-cell's listening cycle.

In step 43, at least some of the SA-cells that received and measured theIRMs may be configured to wirelessly transmit messages containing theirresponses to the terminal, e.g. via a channel on the requested RATand/or frequency, or via a common information request response channel(which could be designed specifically for the purpose). Such messagescould include at least a portion of the measured results to the terminal15 (e.g. the measured signal strength and/or the estimated path lossdetermined by the SA-cell). The SA-cells may also be configured toinclude in their messages an indication to what extent the SA-cell iscapable and able to provide the requested service. Further, the SA-cellsmay be configured to include additional information regarding theircurrent load and/or their currently available resources (e.g. RAT,frequency or frequency band, codes) and/or may further propose specificresources, which resources the SA-cell provisionally reserves for thecase the terminal would select the SA-cell.

The SA-cell may be configured to only transmit a message regarding someIRMs. For example, the SA-cell may be configured to not transmit amessage to the terminal if the SA-cell cannot provide the servicerequested by the IRM. Alternatively, the SA-cell could be configured toprocess and transmit response messages even regarding such IRMs, with anindication that the SA-cell is unable to provide the service and,optionally, an indication of what the SA-cell is capable of and able toprovide, as described above.

In an embodiment, if the SA-cell is able to support the servicerequested in the received IRM, the SA-cell may provisionally reserve theresources according to the requested service and also inform theterminal about it. Such provisionally reserved resources may be freed upafter a suitable period (e.g. when a timer expires) or when the SA-cellis informed that its service is not needed for this particular servicerequest.

In an embodiment, the responding SA-cell may be configured to apply asmall controlled delay between the moment the IRM is received and themoment the corresponding response message is transmitted (and, whenapplicable, also to control the time between repeated response messagesto a sequence of IRMs). By controlling the delay in dependence of e.g.the strength of the signal with which the SA-cell received the IRM fromthe terminal, a potentially better candidate SA-cell can be made torespond earlier than a potentially worse candidate SA-cell, thussupporting the terminal's function of receiving the response messagesand of selecting the best candidate SA-cell.

Because more than a single SA-cell may respond at about the same time tothe same IRM from the terminal, it is desirable that there is amechanism to cope with response messages from multiple SA-cells arrivingat the terminal overlapping (simultaneously) or partially overlapping.This may be achieved, for example, by configuring the different (e.g.neighboring) SA-cells to use different channel codes and configuring theterminal 15 to simultaneously monitor multiple different channel codes,possibly all of the different channel codes. This may also be achievedby multiple (repeated) transmissions of a same response message from anSA-cell at separate moments, separated by different (e.g. randomized orSA-cell-dependent) delays.

In an embodiment of step 43, the SA-cells may be configured towirelessly transmit messages containing their responses to the terminalnot directly but via the LA-cell that the terminal is camping on. Insuch an embodiment, the SA-cells would first transmit their responses tothe LA-cell and the LA-cell then would provide to the terminal one ormore reports containing at least some of the information received in theresponses from the SA-cells. For example, the LA-cell may provide to theterminal and aggregate reports for all of the SA-cells that providedresponses regarding received IRMs.

In an embodiment, based on the responses received from the SA-cells, theterminal 15 may be configured to maintain a list of at least the mostrecent and most relevant results for the measured signals together withthe indication of the corresponding SA-cells.

Further, the embodiments of Solution #2 could be combined with theSolution #1 in that the terminal 15 may perform the method steps 41-43but then, instead of making the selection of the SA-cell itself, providea report regarding the measurements to the decision unit 11, similar tothe step 33 described in the Solution #1. Such a report could include atleast some of the information provided to the terminal by the SA-cellsthat received and processed the IRM transmitted by the terminal. Thedecision unit 11 could then select one or more SA-cell for establishingthe data connection with the terminal based on this report, similar tothe step 34 described in the Solution #1. A person skilled in the artwould readily recognize how to adapt the discussions of steps 33 and 34to this embodiment and, therefore, in the interests of brevity, thesediscussions are not repeated here.

Continuing with the method illustrated in FIG. 6, in step 44, based, atleast partially, on the information received in the response messagesfrom one or more SA-cells, the terminal 15 selects (assigns) one or moreSA-cell from the candidates for establishing the data connection. Thecandidates may include not only the SA-cells that provided theirresponse to the terminal, but also the SA-cells that didn't providetheir responses and the SA-cells that didn't even receive the IRM. Thiscould be used e.g. when the terminal is configured to monitor activeSA-cells and to evaluate whether the monitored active SA-cellsconstitute suitable candidates for establishing the data connectionwith. In other words, in addition to the information received in theresponse messages, the terminal 15 may also take into consideration,when selecting a SA-cell, information regarding other SA-cells that didnot provide responses.

The terminal 15 may further be configured for establishing the dataconnection (i.e., setting up a traffic channel) with the selected one ormore SA-cell. Further, a route for the traffic (and the associatedsignaling) may be set up connecting the selected one or more SA-cell andthe network.

Further, the terminal 15 and/or the SA-cells and/or the network may befurther configured to inform the non-selected SA-cell(s), which may thenrelease the provisionally reserved resources for fulfilling the request.For example, once a data connection has been established between theterminal and the selected SA-cell, the terminal may provide the SA-cellidentities of the non-selected SA-cells to the selected SA-cell and theselected SA-cell may then inform the non-selected SA-cells accordingly.

In a cellular wireless telecommunication system it may happen that aterminal in active mode, having a connection with a particular cell,moves out of (the coverage area of) that cell and into (the coveragearea of) another cell. Then a so-called handover (handoff) may beperformed, meaning that the connection between the terminal and thecurrent cell (source cell) is transferred (handed over) to a connectionbetween the terminal and a different cell (target cell).

Solution #2 as described above may also be used in an energy-efficientwireless network to facilitate a handover of the data connection betweenan active terminal and the SA-cell it has established the dataconnection with to another, different, SA-cell.

An active terminal may emit an IRM as described above, e.g. periodicallyand/or when the signal received from the SA-cell it has established adata connection with drops below a predetermined threshold and/or whentriggered by the network. The terminal may evaluate the informationcontained in the response messages received from the SA-cells and,taking into account considerations similar to the ones described above,select a different SA-cell as target SA-cell for a handover.

As described above, the terminal may further inform the network and/orLA-cell and/or the involved (source and target) SA-cells.

Solution #3: Session Setup Via Sa-Cells Measuring Signal Transmitted bythe Terminal in Idle Mode and the Network Selecting the Sa-Cell Based onthe Measurements

Similar to the solutions #1 and #2 described above, in the context asillustrated in FIGS. 3 and 4, the terminal 15 is assumed to be an idleterminal which may, in the future, have to transfer to an active mode,either because it receives a page (e.g. from the LA-cell the terminalcamps on, e.g. the LA-cell 12) or because the terminal 15 (possibly viathe user of the terminal) initiates exchange of user data. Similar tothe solutions #1 and #2, embodiments of the solution #3 also address theproblem of selecting (assigning) a suitable SA-cell (one already activeor one currently in power-save mode) for that terminal.

Similar to the solution #2, embodiments of solution #3 are based on theidea that a terminal in the idle mode is configured to emit the IRMintended to be received by one or more of the SA-cells in thetelecommunications network and that at least some of the SA-cells may beable to receive the IRM transmitted by the terminal and determine thesignal strength with which they received the IRM. At least some of thoseSA-cells that determined the signal strength of the received IRM canthen provide messages to the decision unit reporting the determinedsignal strength. At least partially based on such messages received fromthe SA-cells, the decision unit can then make a selection of one or moreof the most appropriate SA-cells for the terminal to establish the dataconnection with.

In this manner, the terminal 15 facilitates establishment of the dataconnection between the terminal 15 and one of the SA-cells by enablingthe SA-cells to obtain information indicative of the propagationconditions between the terminal 15 and various SA-cells (e.g., signalstrength). Since the SA-cells then report the results of theirmeasurements to the decision unit (which could possibly be includedwithin the LA-cell), the selection of at least one SA-cell for theterminal may be centrally managed.

FIG. 7 sets forth a flow diagram of method steps for selecting one ormore of the SA-cells 13, 14 when the terminal 15 transmits an IRM andthe decision unit 11 makes the selection of the most appropriateSA-cell, according to one embodiment of the present invention. While themethod steps are described in conjunction with FIG. 3, persons skilledin the art will recognize that any system configured to perform themethod steps, in any order, is within the scope of the presentinvention.

The method begins in step 51 where the terminal 15 in an idle modetransmits an IRM. In one embodiment, the terminal 15 may be configuredto transmit the IRM at some predetermined times and/or at somepredetermined pattern, even though there is no immediate need toestablish a data connection with any of the SA-cells. In otherembodiments, the terminal 15 may be configured to transmit the IRM whenthe terminal receives an indication that the data connection between theterminal and one of the SA-cells should be established. Such anindication could e.g. be a paging message received from the LA-cell 12on which the idle terminal 15 is camping or be an indication from theuser of (or an application running on) the terminal wishing to exchangeuser data over the established data connection.

In one embodiment, the IRM may be transmitted via a broadcast channel.The IRM is not intended for and not directed towards the LA-cell (asopposed to e.g. a service request message typically used in conventionalnetworks) but is intended for SA-cells which may potentially provideservice to the terminal 15. To that end, the IRM could also includeinformation indicative of the request of the terminal for establishing adata connection between the terminal and one of the SA-cells.

In an embodiment, the terminal may be configured to include in the IRMan identification of the network to which the terminal belongs. Byproviding such identification in the IRM, the SA-cell receiving the IRMcan differentiate between the IRMs received from terminals belonging todifferent networks and then choose whether or not to respond. Forexample, the SA-cell may choose not to respond when the IRM is sent by aterminal in a competitor's network. In this case, the providedidentification does not need to be terminal-specific. It would besufficient to only identify the network that the terminal belong to.

The IRM may also include an indication of access priority. For example,an emergency response terminal or a consumer terminal making anemergency call may include an indication of high access priority or anM2M terminal (e.g. electricity meter) may include an indication of lowaccess priority. By providing such an indication in the IRM, the SA-cellreceiving the IRM can differentiate between the IRMs received fromterminals and/or purposes having different access priorities and thenchoose whether or not to respond.

Further, the IRM should be such as to allow the receiving SA-cell todetermine the signal strength with which the IRM is received and/or toestimate the path loss between the terminal and the receiving SA-cell.

Optionally, the IRM may include an indication of the service(s)requested and/or the terminal capabilities, which may be relevant to aSA-cell receiving the IRM in determining to what extent the SA-cell iscapable and able to provide the requested service. The terminalcapabilities that could be indicated in the IRM include e.g. one or moreof supported frequency band(s), supported RAT(s), supported mode(s),power with which the IRM is sent by the terminal, supported (maximum)terminal power, and requested (minimum) bit rate.

In various embodiments, similar to the solution #2, the terminal 15 maytransmit the IRM with a relatively high power (e.g. at the maximumterminal's transmitting power or at still relatively high power, butlower than the maximum power) in order to maximize the likelihood thatat least one suitable SA-cell is able to detect the IRM.

Also similar to the solution #2, the terminal 15 may be configured totransmit the IRM more than once in a sequence, where the subsequent IRMsin the sequence may be transmitted with increased or with increasingpower and/or with a randomized delay relative to the preceding IRM inthe same sequence.

In step 52, at least some of the SA-cells may receive the IRMtransmitted by the terminal and process the IRM by at least determiningthe signal strength with which the IRM is received. All of thediscussions provided above regarding step 42 of solution #2 (i.e., thedescription after the introduction of step 42 and before theintroduction of step 43) are applicable to step 52 shown in FIG. 7 and,in the interests of brevity, are not repeated here.

In step 53, at least some of the SA-cells that received and measured theIRMs may be configured to transmit messages containing their responsesto the decision unit, e.g. via backhaul links typically found betweeneach of the SA-cells and the network and between the LA-cell and thenetwork and/or via other links providing a same interconnection betweenSA-cells and the LA-cell, if the decision unit 11 is a part of theLA-cell 12. Such messages could include information regarding at least aportion of the measured results (e.g. the measured signal strengthand/or the estimated path loss determined by the SA-cell). In addition,the SA-cells may supplement the message with additional information suchas the identity of the SA-cells and/or with an indication of the timewhen the IRM was received by the SA-cell. The SA-cells may also beconfigured to include in their messages an indication to what extent theSA-cell is capable and able to provide the requested service. Further,the SA-cells may be configured to include additional informationregarding their current load and/or their currently available resources(e.g. RAT, frequency or frequency band, codes) and/or may furtherpropose specific resources, which resources the SA-cell provisionallyreserves for the case the terminal would select the SA-cell.

If the IRM included information allowing an identification of theterminal provided in any of the manners described in association withsolution #2, then the SA-cell may be configured to detect thatinformation and to forward it to the decision unit 11. If the decisionunit 11 receives (potentially a lot of) messages from the SA-cells thatrelate to requests from different terminals, receiving such informationthat allows the decision unit to identify the IRM and/or the terminalthat transmitted the IRM may be particularly useful. For example, thedecision unit 11 may be able to identify the IRM and/or the transmittingterminal by receiving, from the SA-cell, information related to the timeof reception of the IRM, to the channel on which or the channel codewith which it was received, and/or to the contents of the IRM, which mayinclude, e.g. a (partial) terminal identification and/or some kind ofreference (tag or label) inserted in the IRM by the terminal. This wouldallow the decision unit to relate all received messages (received with acertain time frame) with a particular combination of partial ID and/or areference (tag, label) to each other.

Similar to the solution #2, the SA-cell may be configured to transmitmessages to the decision unit only regarding some IRMs. For example, theSA-cell may be configured to not transmit a message to the decision unitif the SA-cell cannot provide the service requested by the terminal.Alternatively, the SA-cell could be configured to process and forwardmessages even regarding such IRMs, with an indication that the SA-cellis unable to provide the service and, optionally, an indication of whatthe SA-cell is capable of and able to provide, as described above.

In an embodiment, if the SA-cell is able to support the servicerequested in the received IRM, the SA-cell may provisionally reserve theresources according to the requested service and also inform thedecision unit about it and may, optionally, also inform the terminal.Such provisionally re-served resources may be freed up after a suitableperiod (e.g. when a timer expires) or when the SA-cell is informed thatits service is not needed for this particular service request.

In step 54, based, at least partially, on the information received inthe messages from one or more SA-cells, the decision unit 11 isconfigured to select (assign) one or more SA-cell from the candidatesfor the terminal to establish the data connection with. The candidatesmay include not only the SA-cells that provided their response to thedecision unit, but also the SA-cells that didn't provide their responsesand the SA-cells that didn't even receive the IRM. This could be usede.g. when the decision unit is configured to obtain informationregarding active SA-cells via e.g. steps 31-33 illustrated in FIG. 5 anddescribed above. When decision unit 11 has such information, it is ableto evaluate whether the monitored active SA-cells constitute suitablecandidates for the terminal to establish the data connection with. Inother words, in addition to the information received in the messagesfrom the SA-cells, the decision unit 11 may also take intoconsideration, when selecting a SA-cell, information regarding otherSA-cells that did not provide responses.

Once one or more SA-cells are selected by the decision unit 11 as themost appropriate SA-cells for establishing the data connection with theterminal, the decision unit 11 may indicate the selected SA-cells to theterminal. In one embodiment, such indication may be provided via theLA-cell (e.g. in response to receiving a SRM received from the terminalvia the LA-cell). This could be particularly useful when the IRMtransmitted by the terminal and forwarded by the SA-cells to thedecision unit 11 contains a terminal identity suitable to uniquelyaddress the terminal in the LA-cell or when the IRM contains the partialterminal ID and/or reference (tag or label) the terminal used in theIRM, such that the LA-cell/decision unit is able to reconcile the IRM(and therewith possibly the full terminal ID) with the result of theselection. In another embodiment, such indication may be provided viaone or more of the selected SA-cells. The latter embodiment assumes thata channel (with mutually known resource details) between the terminaland the selected SA-cell can be made available, along which channel anSA-cell may initiate the set up of a data connection to the terminal.Also in this embodiment the terminal ID or the partial terminal IDand/or the reference (tag or label) may facilitate the terminal toreceive and recognize the indication for the terminal.

The terminal 15, in response to receiving the indication regarding theselected SA-cell, may further be configured for establishing the dataconnection (i.e., setting up a traffic channel) with the selected one ormore SA-cell. Further, a route for the traffic (and the associatedsignaling) may be set up connecting the selected one or more SA-cell andthe network.

Once the decision unit 11 knows the identities of the selected SA-cells,the decision unit 11 may assist in and prepare for setting up the routefor the traffic connecting the selected SA-cell and the network. Thismay also be performed by LA-cell 12 when decision unit 11 is within theLA-cell or when the decision unit provides the information to theLA-cell.

Further, the decision unit 11 may be further configured to inform thenon-selected SA-cell(s), which may then release the provisionallyreserved resources for fulfilling the request.

If any of the selected SA-cells are in a power-save mode, the decisionunit 11 may further be configured to activate the selected SA-cells(possibly via the LA-cell).

In a cellular wireless telecommunication system it may happen that aterminal in active mode, having a connection with a particular cell,moves out of (the coverage area of) that cell and into (the coveragearea of) another cell. Then a so-called handover (handoff) may beperformed, meaning that the connection between the terminal and thecurrent cell (source cell) is transferred (handed over) to a connectionbetween the terminal and a different cell (target cell).

Solution #3 as described above may also be used in an energy-efficientwireless network to facilitate a handover of the data connection betweenan active terminal and the SA-cell it has established the dataconnection with to another, different, SA-cell.

An active terminal may emit an IRM as described above, e.g. periodicallyand/or when the signal received from the SA-cell it has established adata connection with drops below a predetermined threshold and/or whentriggered by the network. The SA-cells receiving the IRM may forwardtheir messages to the decision unit.

The decision unit may evaluate the information contained in the messagesreceived from the SA-cells and, taking into account considerationssimilar to the ones described above, select a different SA-cell astarget SA-cell for a handover.

As described above, the decision unit may further inform the terminaland/or the LA-cell and/or the involved (source and target) SA-cells.

One embodiment of the invention may be implemented as a program productfor use with a computer system. The pro-gram(s) of the program productdefine functions of the embodiments (including the methods describedherein) and can be contained on a variety of, preferably non-transitory,computer-readable storage media. Illustrative computer-readable storagemedia include, but are not limited to: (i) non-writable storage media(e.g., read-only memory devices within a computer such as CD-ROM disksreadable by a CD-ROM drive, ROM chips or any type of solid-statenon-volatile semiconductor memory) on which information is permanentlystored; and (ii) writable storage media (e.g., floppy disks within adiskette drive or hard-disk drive or any type of solid-staterandom-access semiconductor memory, flash memory) on which alterableinformation is stored. The computer program may be run on the processorsdescribed herein.

What is claimed is:
 1. In a telecommunications system comprising a decision unit, an LA-cell base station, and a plurality of SA-cell base stations, a method for a terminal to facilitate establishment of a data connection between the terminal and at least one of the plurality of the SA-cell base stations, while at least one of the plurality of the SA-cell base stations is in power saving mode, the LA-cell base station optimized to exchange signaling messages with the terminal and the SA-cell base stations each optimized to exchange user data with the terminal, the method comprising: while the terminal is in an idle mode and is camping on the LA-cell base station, the terminal determining properties of a signal received from each of one or more SA-cell base stations of the plurality of SA-cell base stations, the properties being indicative of propagation conditions between each of the one or more SA-cell base stations and the terminal; while the terminal is in the idle mode and is camping on the LA-cell base station, the terminal providing a report to the decision unit, via the LA-cell base station, the report comprising at least information indicative of at least a portion of the determined properties for at least one of the one or more SA-cell base stations; while the terminal is in an idle mode and is camping on the LA-cell base station, the terminal receiving an indication that the data connection is to be established between the terminal and a selected SA-cell base station of the plurality of SA-cell base stations, wherein the selected SA-cell base station is selected by the decision unit at least partially based on the report.
 2. The method according to claim 1, wherein, for each of the one or more SA-cells, the determined properties comprise a signal strength of the signal received from the each of the one or more SA-cells and/or a path loss estimate.
 3. The method according to claim 1, wherein when at least two SA-cell base stations of the one or more SA-cell base stations are in a power-save mode, each of the at least two SA-cell base stations transmits the signal to the terminal in a predetermined pattern.
 4. The method according to claim 3, wherein the predetermined pattern for the each of the at least two SA-cell base stations is such that the terminal receives the signals from each of the at least two SA-cell base stations substantially contemporaneously.
 5. The method according to claim 3, wherein the predetermined pattern for the each of the at least two SA-cell base stations is such that the terminal receives the signals from each of the at least two SA-cell base stations in a succession.
 6. The method according to claim 1, wherein the terminal is in a power-save mode and the method further comprises the terminal exiting the power-save mode to receive the signal from the each of the one or more SA-cell base stations and/or to determine the properties of the signal received from the each of the one or more SA-cell base stations.
 7. A terminal comprising means for performing the steps of claim
 1. 8. A non-transitory computer readable medium having stored thereon a computer program comprising software code portion configured, when executed by a processor, for performing the steps of claim
 1. 9. A decision unit comprising a processor, the processor configured at least for: receiving from a terminal in idle mode camping on a LA-cell base station a report comprising at least information indicative of at least a portion of properties determined for at least one of a plurality of SA-cell base stations, the terminal determining properties of a signal received from each of one or more SA-cell base stations of the plurality of SA-cell base stations, the properties being indicative of propagation conditions between each of the one or more SA-cell base stations and the terminal, the LA-cell base station optimized to exchange signaling messages with the terminal and the SA-cell base stations each optimized to exchange user data with the terminal, and based at least partially on the report, selecting at least one SA-cell base station of the plurality of SA-cell base stations for establishing the data connection between the terminal and the selected SA-cell base station.
 10. The decision unit according to claim 9, wherein the processor is further configured for providing an indication to the terminal that the data connection is to be established between the terminal and the selected SA-cell base station.
 11. The decision unit according to claim 10, wherein the indication is provided in response to receiving a service request message from the terminal, via the LA-cell base station, requesting establishment of the data connection.
 12. The decision unit according to claim 9, wherein the processor is further configured for, when at least one SA-cell base station of the one or more SA-cell base stations is in a power-save mode and in response to receiving a service request message from the terminal, providing a transmit-trigger to the at least one SA-cell base station to transmit the signal.
 13. The decision unit according to claim 12, wherein the transmit-trigger is at least partially based on one or more of a terminal location estimate, an estimate of the accuracy of the terminal location estimate, and activity status of the SA-cell base stations in the vicinity of the estimated terminal location.
 14. An LA-cell base station comprising the decision unit according to claim
 9. 